Field of the Invention
The invention relates to a method for evaluating the quality of a television picture.
Reception poses no appreciable difficulty in stationary television receiving stations because the reception conditions are largely constant. By contrast, the reception conditions in mobile receiving stations can fluctuate considerably depending on the nature of the terrain being traveled through, because momentary interference pulses and echo pulses can occur. In the meantime, motor vehicles, such as e.g. passenger cars and touring coaches, but also railroad vehicles are being equipped with television receivers and screens in order to be able, on the one hand, to display messages, for example traffic messages communicated via teletext, or, on the other hand, to entertain travelers with television programs. The reception conditions in a moving receiving station fluctuate considerably, under certain circumstances, owing to the terrain currently being traveled through; these reception conditions mean that great strain is put on traveling television viewers' eyes, in an unpleasant manner, because the picture quality can fluctuate to a considerable extent. If the vehicle travels through a radio shadow, for example, all the viewer sees on the screen is noise. Viewing a television program subjected to such interference is more likely to lead to the viewers becoming tired than serve to entertain them.
It is known to improve the reception of radio signals in mobile receiving stations by means of multipath reception, referred to as "diversity". Space diversity is understood to mean a system having a plurality of receivers which receive identical signals, e.g. the same television program, at identical frequencies. Frequency diversity is understood to mean a system likewise comprising a plurality of receivers, which receive identical signals, e.g. the same television program, at different frequencies. In a diversity system, the receiver which has the best reception in each case is selected according to some criterion. For a diversity reception system having a plurality of receivers, therefore, it is necessary to provide a criterion for selection of the receiver which has the best reception.